Needle valves are often employed to control flow of a fluid. Needle valves are particularly suited for controlling fluid flow to a gas analyzer such as a sensor for measuring COx, HH3, NOx, O2, SOx, etc. While generally effective for controlling fluid flow to gas analyzers, the test fluid can often be contaminated by environmental fluids introduced into the test fluid through the needle valve.
Efforts to seal needle valves against the introduction of environmental air into a fluid flowing through the valve have resulted in significant improvement, but have practical limitations, size considerations and/or cost considerations which render even the most carefully constructed needle valve insufficient or impractical for certain applications requiring detection of contaminants at concentrations at less than parts per million (ppm).
Accordingly, a need exists for a needle valve capable of preventing the introduction of even minute amounts of environmental air into a fluid flowing through the valve.